This invention relates to a polyurethane adduct comprising a structo-terminal carboxylic acid group. More specifically this invention relates to an adduct which contains a plurality of internal urethane linkages, and which additionally bears one or more terminal carboxylic acid groups per molecule.
In general, urethane-containing adducts are prepared by reacting an organic polyisocyanate with an active hydrogen-containing substance. The reaction may be conducted in the presence of a solvent and various addition sequences of isocyanate with active hydrogen-containing substances employed so as to arrive at an end product that can be substantially free of any isocyanate functionality or isocyanate-reactive functionality such as disclosed in U.S. Pat. No. 4,079,028. The products disclosed are essentially non-reactive products having value as a rheology modifying agent in various application areas including paint compositions and cosmetics. However it is noted that the procedure of preparing adducts as reported in U.S. Pat. No. 4,079,028 is deficient with respect to control of molecular weight build-up leading to undesirable gelation or solids formation. Liquid adducts are generally favored for convenience of industrial processes.
There is now a desire to modify such adducts and provide alternative molecules that are "tailored" to perform multiple tasks whereby their rheological characteristics can be exploited in other application areas including, for example, surface protection and adhesives. By surface protection, it is understood the protection of a surface by coating that surface with a protective substance. By adhesive, it is understood the bonding of a first surface to a second surface that can be of a like or different substrate. In conventional surface coating chemistry and adhesion technology, frequently many different molecules are used in sequence or in combination to achieve the desired end result. Accordingly, it would be attractive to provide an alternative molecule which can reduce, or even overcome, the need to use multiple molecules. It would further be desirable to be able to prepare such alternative molecule by a process devoid of the deficiencies of the above noted art procedure.
To this purpose, the present investigations have been directed to the preparation of polyurethane adducts, preferably being a liquid at room temperature, which are functionalized with carboxylic acid groups at the end of the polymer chains. As carboxylic acids are reactive towards the isocyanate moiety it has been necessary to develop a synthetic procedure which provides for the formation of a polymer containing urethane linkages and carboxylic acid functionality.